Baffle design for a gas-fired unit heater

ABSTRACT

A gas-fired unit heater ( 10 ) is provided and includes a burner ( 20 ), a heat exchanger tube ( 18 ) located to receive a flow of the combustion products from the burner ( 20 ), the tube ( 18 ) including at least one linear tube run ( 30 ) extending along a longitudinal axis ( 18 ), and a corrugated baffle ( 40 ) received in the tube run ( 30 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to provisional application Ser. No.60/664,878, filed Mar. 24, 2005, entitled “Improved Baffle Design for aGas-Fired Unit Heater”.

BACKGROUND OF THE INVENTION

Gas-fired unit heaters are known and are commonly used to heatrelatively large open and closed areas, such as residential andcommercial garages or warehouses. Such units will often include aplurality of gas burners that combust natural or propane gas, with theheated combustion products being drawn through one or more heat exchangetubes by a exhaust blower or fan. Heat is transferred from thecombustion products or flue gas to air that is passing over the exteriorof the heat exchanger tubes, with the heated air then flowing into thearea that is to be heated.

Given the ever-increasing cost of heating fuel, such as natural and/orpropane gas, there is a continuing need to improve the efficiency ofsuch unit heaters, this includes the efficiency of the transfer of heatfrom the combustion products to the air passing over the exterior of thetube.

SUMMARY OF THE INVENTION

In accordance with one form of the invention, a gas-fired unit heater isprovided and includes a burner, a heat exchanger tube located to receivea flow of the combustion products from the burner, the tube including atleast one linear tube run extending along a longitudinal axis, and acorrugated baffle received in the tube run. The tube run has an innerwail.

The baffle includes a corrugated strip of material having a lengthextending parallel to the longitudinal axes, with alternating peaks andvalleys joined by side walls defining corrugations along the length andeach of the peaks and valleys extending non-parallel to the longitudinalaxis. In a preferred form, the peaks and valleys extend perpendicular tothe longitudinal axis.

In one feature, opposite edges of the strip engage the inner wall of thetube run at at least one of the peaks and at at least one of thevalleys.

In one feature, the inner wall is cylindrical with an inside diameter D.The corrugations have a height dimension H from the peaks to the valleysperpendicular to the longitudinal axis, and a width dimension Wperpendicular to both the height dimension and the longitudinal axis.The ratio of (W×H)/D is in the range of 0.60 to 0.80. In a highlypreferred embodiment, the ratio of (W×H)/D is 0.66 within the range ofnormal manufacturing tolerances.

In one form, the gas-fired unit heater includes a blower and isconfigured to provide a volumetric flow rate of the combustion productsthrough the heat exchanger tube in the range of 2 cubic feet per minute(cfm) to 8 cfm under normal operating conditions, with a preferredoptimum of 5 cfm.

As one feature, the inner wall includes a recess and the corrugatedstrip of material includes a longitudinal end tab that is configured toengage in the recess to retain the baffle within the tube run. In afurther feature, the recess is an annular relief in the inner wall ofthe tube run adjacent an outlet end of the tube run.

Other objects, advantages, and features of the invention will becomeapparent from a detailed review of the specification, including theappended claim and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a unit heater including a baffleconstructions embodying the present invention;

FIG. 2 is a perspective view of selected components of the unit heaterof FIG. 1;

FIG. 3 is a reduced size, perspective view of a plurality of heatexchanger tubes of the unit heater of FIG. 1;

FIG. 4 is a plan view of the heat exchanger tubes of FIG. 3;

FIG. 5 is a side elevation of the heat exchanger tubes of FIG. 3;

FIG. 6 is an end view of the heater exchanger tubes of FIG. 3;

FIG. 7 is a reverse angle perspective view of the components of FIG. 2with a heat exchanger tube broken away to reveal a baffle;

FIG. 8 is an enlarged section view of any one of the tubes taken fromthe line 8-8 in FIG. 5;

FIG. 9 is a perspective view of one form of the baffle of FIG. 8 shownin smaller scale than FIG. 8;

FIG. 10 is a side view of the baffle of FIG. 9 shown in larger scalethan FIG. 9;

FIG. 11 is a view taken from line 11-11 in FIG. 10;

FIG. 12 is an enlarged section view of any of the tubes taken from theline 12-12 in FIG. 4 and showing another form of the bracket embodyingthe present invention;

FIG. 13 is a view taken from line 13-13 in FIG. 12;

FIG. 14 is a section view taken from line 14-14 in FIG. 12;

FIG. 15 is a side elevation view of the baffle of FIG. 12, removed fromthe tube run; and

FIG. 16 is a section view of the burner box looking towards the inletsto the burners.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A unit heater 10 is shown in FIG. 1 and includes an outer housing 12with a hot air outlet 14 that includes a plurality of louvers 16 (onlyone shown in FIG. 1) with a plurality of heat exchanger tubes 18 locatedwithin the housing 12 behind the outlet 14 such that air is heated as itflows over the heat exchanger tubes 18 and passes from the outlet 14into an area or room to be heated. It should be understood that whilethe invention is described in connection with the illustrated embodimentof a unit heater 10, no limitation to a specific type or construction ofunit heater is intended unless expressly recited in the claims.

With reference to FIG. 2, the unit heater 10 includes a plurality ofburners 20 (only one shown in FIG. 2), each aligned with an inletopening 22 for a corresponding one of the heat exchanger tubes 18 suchthat hot combustion products from each of the burners 20 is received inthe corresponding tube 18. The burners 20 are housed within a burner box23, only part of which is shown in FIG. 2. The unit heater 10 furtherincludes a fan or blower (power exhauster) 24 that draws the combustionproducts through the heat exchanger tubes 18 and blowing the combustionproducts (flue gases) from a flue collecting chamber 25 that gathers thecombustion products as they exit each of the heat exchanger tubes 18.The blower 24 also serves to draw air into the unit heater 10 forcombustion with the gas at the burners 12.

Each of the heat exchangers tubes 18 includes one or more linear tuberuns 30, and in the case of the illustrated embodiment in FIGS. 1-7,each of the heat exchangers tubes 18 includes four linear tube runs 30A,30B, 30C and 30D, with tube bends 32A, 32B and 32C connecting the tuberuns 30A, 30B, 30C and 30D, as best seen in FIG. 3. Each of the tuberuns 30A-30D extends along a corresponding longitudinal axis 33, asshown for the tube runs 30D in FIG. 3. Each of the tubes 18 furtherincludes an inlet end 34 at the end of the tube 18 opposite from anoutlet end 36. It should be appreciated that by providing four of thetube runs 30 for each of the heat exchanger tubes 18, the inlet andoutlet ends 34 and 36 can be located in the same plane. It should alsobe appreciated that an odd number of tube runs 30 would allow for theends 34 and 36 to be located in spaced planes.

As best seen in FIG. 7, a corrugated or wave baffle 40 is provided inthe tube run 30 d of each of the heat exchanger tubes 18. It has beenfound that the baffle 40 improves the heat transfer efficiency of theunit heat 10. As best seen in FIGS. 9-12, The baffle 40 is preferableformed by a strip 42 of material having a length L extending parallel tothe longitudinal axis 33, with alternating peaks 44 and valleys 46joined by side walls 48 defining waves or corrugations 50 along thelength L. Each of the peaks 44 and valleys 46 extends non-parallel, andpreferably perpendicular, to the longitudinal axis 33. The corrugationshave a height dimension H from the peaks 44 to the valleys 46perpendicular to the longitudinal axis 33 and a width dimension Wperpendicular to both the height dimension H and the longitudinal axes33 It is preferred for the corrugations 50 to be sized and configured sothat opposite edges 52 of the strip 42 engage an inner wall 54 of thetube run 30D at at least one of the peaks 44 and at at least one of thevalleys 46. In this regard, each of the adjacent side walls have anangular spacing α which is preferably the same for each of thecorrugations 50, except for one or more of the middle corrugations 50which may have a smaller angle α so as to create the desired engagementof the side edges 52 of the strip. This engagement can reduce or preventrattling of the baffle 40 in the corresponding tube 18.

In a preferred embodiment, the angles α are in the range of 102 degreesto 121 degrees, with a preferred optimum of 109 degrees.

With or without the desired engagement, it is also preferred that theratio of the multiple of the width W and the height H to the diameter D[(W×H)/D] be in the range of 0.60 to 0.80 with an optimum being at 0.66within the standard manufacturing tolerances of the baffle 40 and tube18. These ranges create a desirable amount of free flow area 55(illustrated with cross hatching in FIG. 8) between the baffle 42 andthe inner wall 54 of the tube run 30D.

Preferably, the strip 42 is a strip of sheet metal with bends formingthe alternating peaks 44 and valleys 46 of the corrugations 50

With reference to FIGS. 9, 10 and 11, the illustrated baffle 40 furtherincludes a mount flange 56, which in the illustrated embodiment is partof the strip 42, and which extends outside of the outlet end 36 of thecorresponding tube 18 so that it can be joined to the housing 12 using asuitable fastener (not shown) which extends through a mount hole 58 inthe flange 56 to engage the housing 12. This structure retains thebaffle 40 in the tube run 30D.

With reference to FIGS. 12-15, another embodiment of the baffle 40 isshown wherein the flange 56 is replaced by a longitudinal end tab 60that is configured to engage in an annular recess 62 of the tube 18 witha spring force that is reacted through the baffle 40 to the edges 52 ofthe strip 42 that engage the inner wall 54 of the tube run 30D to retainthe baffle 40 in the tube 18. This design has the benefit of beingeasily installed and not requiring a separate fastener. This design alsocan reduce or prevent rattling between the baffle 40 and thecorresponding tube 18.

The blower 24 is sized to provide the movement of the combustionproducts from the flue collecting chamber 25 while sustaining the draftfor the combustion process and entraining air for the combustionprocess. To accomplish this, the blower 24 must overcome the pressureresistance caused by the heat exchange tubes 18, the baffles 40, thecollecting chamber 25, the restriction of any vent associated with thechamber 25 or flue, the restriction associated with any vent terminal,and any reasonable natural external force. In this regard, in onepreferred form, the blower 24 is sized to create a volumetric flow rateof the combustion products in the range of 2 CFM to 8 CFM through eachof the tubes 18 under normal operating conditions, and in highlypreferred form to deliver 5 CFM.

It should be understood that, while some of the drawings includespecific numbers of the corrugations 50 and specific dimensions ininches and degrees for the baffle 40 and the tubes 18, these dimensionsare for one preferred form of the unit heater 10, and that the specificdimensions and number of corrugations 50 required to optimize theefficiency of the unit heater 10 will be highly dependent upon thespecific parameters of each application, including for example, thenumber of tube runs 30 in each tube 18, the length of the tube run(s) 30including the length of the tube run 30 in which the baffle 40 will beinstalled, the shape of the tube 18, the size of the inner wall 54, andthe desired flow rate of the combustion products through each tube 18.

With reference to FIGS. 2 and 16, another feature is the provision of aburner mount/secondary air bracket 64 that is designed to mount theburners 20 in their appropriate relationship to the tubes 18 whileminimizing the disturbance of the secondary air flow that must flow pastthe burners 20 to the gaps 66 between the outlet ends of the burners 20and the openings 22. In order to provide as complete combustion aspossible, it is important for the secondary air to be as undisturbed aspossible over the entire 360° extent of the gap 66 as the secondary airflows into the combustion products exiting the burners 20 and enteringthe opening 22. To this end, the bracket 64 has been designed so that itis spaced from the side walls 68 of the burner box 23 to provide gaps 70and 72 on either side of the bracket 64, and further have cutouts orwindow openings 74 and 76 so as to allow an air flow through the bracket64 itself while still providing the appropriate structural integrityrequired for the bracket 64.

1. A gas-fired unit heater comprising: a burner; a heat exchanger tubelocated to receive a combustion gas flow from the burner, the tubeincluding at least one linear tube run extending along a longitudinalaxis, the tube run having an inner wall; a corrugated baffle received inthe tube run, the baffle comprising a corrugated strip of materialhaving a length extending parallel to the longitudinal axis, andalternating peaks and valleys joined by side walls defining corrugationsalong the length with each of the peaks and valleys being non-parallelto longitudinal axis.
 2. The unit heater of claim 1 wherein oppositeedges of the strip engaging the inner wall at at least one of the peaksand at at least one of the valleys.
 3. The unit heater of claim 1wherein: the inner wall is cylindrical with an inside diameter D; thecorrugations having a height dimension H from the peaks to the valleysperpendicular to the longitudinal axis and a width dimension Wperpendicular to both the height dimension and the longitudinal axis;and the ratio of (W*H)/D is in the range of 0.60 to 0.80.
 4. Acorrugated baffle for use in a linear tube run of a gas-fired unitheater: the baffle comprising a corrugated strip of material having alength extending parallel to the longitudinal axis, and alternatingpeaks and valleys joined by side walls defining corrugations along thelength with each of the peaks and valleys being non-parallel tolongitudinal axis.
 5. The baffle of claim 4 wherein opposite edges ofthe strip engaging the inner wall at at least one of the peaks and at atleast one of the valleys.
 6. The baffle of claim 4 wherein: the innerwall is cylindrical with an inside diameter D; the corrugations having aheight dimension H from the peaks to the valleys perpendicular to thelongitudinal axis and a width dimension W perpendicular to both theheight dimension and the longitudinal axis; and the ratio of (W*H)/D isin the range of 0.60 to 0.80.